An organic light-emitting diode (OLED) display is one of the hot topics nowadays in the panel display research field. Compared with a conventional liquid crystal display (LCD), the OLED display has advantages of low power consumption, low manufacturing cost, self-luminance, broad angle of view and fast response speed and so on. At present, in a field of displays such as a mobile phone, a personal digital assistant (PDA), a digital camera or the like, the OLED display has started to take place of the conventional liquid crystal display.
Design of a pixel driving circuit is core technical content of the OLED display, and has important research significance. Being different from a thin film transistor (TFT) LCD which controls brightness by utilizing a stable voltage, the OLED display is driven by utilizing current, and thus requires stable current to control light emitting. However, because of influence of TFT manufacturing process, the stability of a threshold voltage of a driving transistor is very poor. Different driving transistors have different threshold voltages while being input a same voltage, such that driving current flowing through different organic light-emitting diodes are different, which further causes the stability of driving current of the OLED display very poor. In the meantime, with the increasing of operating time of the driving transistors, drift would occur to the threshold voltage of driven transistors, thereby further influencing the stability of the driving current. The stability of the driving current would influence the stability of display brightness of the OLED display. Therefore, how to raise the stability of the driving current and then improve uniformity of display brightness of a display device is a problem to be solved urgently by those skilled in the art.